The neural correlates of attention and consciousness

Question 1

The concept of attention

Answer 1

According to William James attention implies withdrawal from some things in order to deal effectively with others ]

Question 2

Visual pathway and field defects

Answer 2

damage to the primary visual cortex V1 causes blindness in the region of the visual field represented by the affected area of cortex

A small unilateral lesion in V1 will lead to scotoma (a small patch of blindness) in one hemifield

Unilateral damage to V1 in its entirety will cause blindness in the whole contralateral visual field (homonymous hemianopia)

total destruction of V1 bilaterally will result in complete cortical blindness

experiments in rhesus monkeys will removal of V1 showed that the monkeys could still respond in simple ways to visual stimuli

Question 3

Blindsight - a disorder of conscious vision

Answer 3

• Occurs following unilateral damage to the primary visual cortex V1
• Above chance visual performance in the ‘blind hemifield’
• Patient may show preservation of
  pupillary reflexes
  manual and saccadic localisation
  wavelength and motion discrimination
  orientation and shape discrimination

Question 4

Perimetric testing in blindsight

Answer 4

patient DB asked to guess if light was presented, remarkably his guesses were correct despite having no conscious perception of the spots of light

Question 5

How does visual information get to the brain in blindsight?

Answer 5

unconscious perception occurs as a result of the 10% of visual information that bypasses the lateral geniculate nucleus and is instead projected to the superior colliculus and pulvinar nucleus of the thalamus which send their axons to other visual areas of the cortex. Because this pathway bypasses the LGN and therefore the primary visual cortex there is no conscious perception

Question 6

What is attention?

selectivity (spatial, temporal, motoric)

Answer 6

processing is limited to just those aspects of sensory input that occupy a particular region of space, or that occur at a particular time

Question 7

What is attention?

capacity limitation

Answer 7

we are unable to simultaneously attend to many inputs in our environment all at once. We can only attend to about 3 or 4 separate objects at a time, and that attention must be redeployed elsewhere if we are to take in more information from a complex scene

Question 8

What is attention?

Vigilance

Answer 8

the period of time for which we can effectively sustain attention

Question 9

What is attention?
Perceptual set (expectation)

Answer 9

we tend to focus our processing resources on stimulus inputs and behaviours that are relevant to the current environment and task demands

Question 10

What is attention?

switching

Answer 10

attention is essential for flexible switching from one task to another, or from one environment to another. Without the ability to switch we would be forced to respond in a stereotypical fashion regardless of task demands or stimuli, an impairment that is sometimes apparent in neurological patients with frontal lobe damage.

Question 11

Covert selective attention

Answer 11

Helmhotz (1821-1894)
large screen with letters, brief electric spark. helmholtz discovered that without moving his eyes he could discriminate all the letters within the attended region

This experiment shows that voluntary allocation of attention can enhance perception of stimuli in a selected region of space, despite the receptors (in this case the retina) remaining fixed